[spankalee]

Something like this <html-include> element should be able to hit all three requirements, if you allow for JavaScript: https://www.npmjs.com/package/html-include-element

[oneeyedpigeon]

I think there are lots of solutions if you allow a JavaScript dependency. In the article, the author demonstrates dynamic 'styling' by just swapping out an image - just like we used to do it back in the 20th century! You could fix the caching problem by dumping your SVG contents into localStorage.